Variation in resistance to the cabbage aphid (Brevicoryne brassicae) between and within wild and cultivated Brassica species

Seven Brassica species were evaluated for their resistance to the cabbage a phid, Brevicoryne brassicae, in a series of field experiments. Four wild Br assica species, two 8 chromosome species with similarities to the B genome of Brassica nigra (Brassica fruticulosa and Brassica spinescens) and two 9 chromosome species containing the C genome (Brassica incana and Brassica vi llosa) were identified as possessing consistently high levels of antibiosis mediated resistance to B. brassicae. None of the species were shown to pos sess consistently high levels of antixenosis resistance. In more detailed g lasshouse experiments one B-like genome species, B. fruticulosa, showed con siderable variation between accessions collected from different sites for r esistance to B. brassicae. In addition, individual accessions of one A geno me species (Brassica rapa) and one C genome species (Brassica alboglabra) w ere shown to be highly variable in their resistance to B. brassicae, some p lants of each accession being highly resistant and others very susceptible. The implications of the variability in resistance to B. brassicae within w ild Brassica species for exploitation in Brassica breeding programmes are d iscussed.